In wireless communication systems, one of the biggest challenges is the increasing need to convey high capacity traffic. For instance, the use of multimedia is increasing. Therefore several different techniques to increase the capacity of communication systems have been presented, such as multiple-input multiple output (MIMO) and space-time transmit diversity (STTD) techniques. Systems based on using multiple antennas are one of the most promising techniques for achieving high data rates for instance in high-speed downlink packet access (HSDPA) systems.
Typically in multi-antenna systems, a transmitter has a plurality of antennas, each of which transmits using the same frequency band and, in the case of wide band code division access (WCDMA) systems, possibly also using the same spreading code. Thus inter-antenna interference becomes very strong and has to be suppressed in a receiver.
A problem is that multi-antenna transmission on a transmitter side and/or multiple antennas on a receiver side cause a large complexity increase in solving coefficients for a channel equalizer of a receiver.